1. Field of the Invention
The present invention relates to an elastic crawler traveling apparatus used for traveling, for example, on a soft ground in construction, civil engineering, agriculture or the like and a sprocket for a crawler belt used in the elastic crawler traveling apparatus.
2. Description of the Prior Art
An elastic crawler traveling apparatus having an elastic crawler formed by an elastic material of rubber or the like is currently used widely in an agricultural machine such as a combine and a construction operation machine such as a back hoe.
Conventionally, the elastic crawler traveling apparatus is mainly constituted by an elastic crawler formed in a shape of an endless belt, a sprocket for a crawler belt to be brought into contact with an inner face of the elastic crawler, a driven wheel, and a rolling wheel.
The sprocket for the crawler belt, the driven wheel and the rolling wheel are arranged at predetermined center distances therebetween and the elastic crawler can be circulatingly run by a transmission of driving force by the sprocket for the crawler belt.
An explanation will be given as follows of the elastic crawler and the sprocket for the crawler belt, the driven wheel and the rolling wheel in reference to FIG. 13 through FIG. 15.
FIG. 13 shows a state in which an elastic crawler and a sprocket for a crawler belt are brought into contact with each other.
An elastic crawler 42 shown in FIG. 13 is mainly constituted by a belt main body 47 in a shape of an endless belt, a plurality of projections 48 formed to project from an inner face of the belt main body 47 and a tension member 49 of a steel cord or the like embedded at an inner portion of the belt main body 47 for restricting elongation of the belt main body 47.
A plurality of the projections 48 are arranged at constant intervals over an entire periphery of the inner face of the belt main body 47.
The tension member 49 is provided for restricting elongation caused by an outwardly pushing force (hereinafter, referred to as extending tension force) exerted by a sprocket 43 for a crawler belt, the driven wheel 45 and the rolling wheel 46 to extend the elastic crawler 42 on the inner face of the elastic crawler 42.
A plurality of the tension members 49 are embedded within a constant embedding width (width designated by notation A, hereinafter, referred to as embedding width A) in a belt width direction (direction indicated by notation X, hereinafter, the direction is defined as a reference direction and the direction is simply referred to as belt width direction) of the belt main body 47.
The sprocket 43 for a crawler belt for driving the elastic crawler 42 is constituted by a drive tooth portion 51 in a rod-like shape fitted to a valley portion between the projections 48 for transmitting the driving force to the elastic crawler 42 and a pair of barrel portion main bodies 50 in a shape of a circular disk for sandwiching the drive tooth portion 51.
As shown by FIG. 13, a length of the drive tooth portion 51 in a longitudinal direction thereof and a root width (width indicated by notation D) of the projection 48 in the belt width direction are made to be substantially equal to each other and the barrel portion main bodies 50 are disposed so as to sandwich the drive tooth portion 51 therebetween.
A contact width in the belt width direction of a portion 56 of the sprocket 43 for the crawler belt in contact with the inner face of the crawler main body 47 is constituted by adding the length in the longitudinal direction of the drive tooth portion 51 and widths in the belt width direction of the barrel portion main bodies 50, and the contact width is indicated by notation E (hereinafter, the width is referred to as contact width E in the sprocket 43 of the crawler belt).
When the length in the longitudinal direction of the drive tooth portion 51 and the root width of the projection 48 are made to be substantially equal to each other as described above, and the drive tooth portion 51 are sandwiched by the barrel portion main bodies 50, in the case in which the elastic crawler 42 and the sprocket 43 for the crawler belt are shifted from each other in the belt width direction, a face on an inner side of the barrel portion main body 50 is brought into contact with the projection 48 to thereby enable to restrict the shift of the sprocket 43 for the crawler belt.
However, since a thickness (a width in the belt width direction) of the drive portion main body 50 is made to be as small as possible for light-weighted formation of the sprocket 43 for the crawler belt and a reduction in material cost, the contact width E in the sprocket 43 for the crawler belt is made smaller than the embedding width A.
A difference between the contact width E of the sprocket 43 for the crawler belt and the embedding width A is indicated by notation F, which is hereinafter referred to as a noncontact width F.
FIG. 14 shows a state in which the driven wheel 45 or the rolling wheel 46 and the belt main body 47 are brought into contact with each other.
In FIG. 14, either of the driven wheel 45 and the rolling wheel 46 constitutes a so-to-speak riding rolling wheel which rolls on an inner peripheral face of the belt main body 47 by riding over the projection 48. A contact width of a portion of the driven wheel 45 (or rolling wheel 46) in contact with the inner face of the belt main body 47 in the belt width direction is indicated by notation G (hereafter, referred to as contact width G in the driven wheel or the like).
Further, in FIG. 14, the contact width E of the sprocket 43 for the crawler belt is shown for comparison.
When the contact width E of the sprocket 43 for the crawler belt is compared with the contact width G of the driven wheel or the like, the contact width E of the sprocket 43 for the crawler belt and the contact width G of the driven wheel or the like are not completely coincident with each other although there are coincident portions thereof.
In this case, the tension member 49 disposed in a range in which the contact width E of the sprocket 43 for the crawler belt and the contact width G of the driven wheel or the like are coincident with each other (overlap each other) (hereinafter, referred to as coincident range) undergoes the extending tension force from the sprocket 43 for the crawler belt, the driven wheel 45 and the rolling wheel 46. However, the tension member 49 disposed outside of the coincident range undergoes the extending tension force only from the sprocket 43 for the crawler belt or only from the driven wheel or the like.
FIG. 15 is a sectional view taken along arrow marks Q—Q of FIG. 13, showing a state in which the elastic crawler 42 is wrapped around the sprocket 43 for the crawler belt.
The elastic crawler 42 is mounted around the sprocket 43 for the crawler belt with being pulled (being applied with tension) in a peripheral direction (direction indicated by notation Y) of the elastic crawler 42 (belt main body 8).
In this case, the rate of elongation caused by the pulling force differs between a portion of the belt main body 47 formed with the projection 48 and a portion thereof between the projections 48.
More specifically, the portion provided with the projection is difficult to elongate since the thickness of the belt main body 47 is thicker by an amount of the projection, while the portion of the belt main body 8 between the projections 48 is readily elongated.
Therefore, when tension is applied along the peripheral direction of the elastic crawler 2, a portion of the tension member 49 which is readily elongated (portion between the projections 9) is pulled to be linear to thereby constitute a form in which the linear portions are connected at the portion difficult to elongate. Accordingly, as shown by FIG. 15, the tension member 49 is deformed into a polygonal shape.
When the tension member 49 disposed in the coincident range is compared with the tension member 49 disposed outside of the coincident range as described above, the tension member 49 disposed in the coincident range undergoes the extending tension force at a plurality of portions by the sprocket for the crawler belt, the driven wheel, and the rolling wheel. Accordingly, a total of the tension member 49 disposed in the coincident range undergoes substantially uniform force, while the tension member 49 disposed outside of the coincident range undergoes local tension force only by the sprocket for the crawler belt or only by the driven wheel 45 (or the rolling wheel 46).
There poses a problem that when the tension member 49 undergoes local tension force as in the tension member 49 disposed outside of the coincident range as described above, the portion undergoing the tension force is liable to break.
Further, since the sprocket 43 for the crawler belt is not brought into contact with the inner face portion of the belt main body 47 (elastic crawler) corresponding to the noncontact width F, the portion is hardly exerted with tension force, whereby the tension force exerted on the tension member 49 disposed within the contact width E in the sprocket for the crawler belt and the tension force exerted on the tension member 49 disposed in the noncontact width F are not uniform.
In this case, the tension member exerted with a greater tension force (tension member disposed in the contact width E of the sprocket for the crawler belt) is liable to break and service life thereof is also shortened.
This is a problem caused by making the length in the longitudinal direction of the drive tooth portion substantially equal to the root width of the projection.
Further, when the tension member 49 is deformed into the polygonal shape, there poses a problem that local tension force is exerted on a portion of a corner in the polygonal shape and the portion is broken.
This is a problem caused by local application of the tension force on the tension member 49.
Hence, it is an object of the invention to provide an elastic crawler traveling apparatus capable of making exertion of local force to a tension member embedded in an elastic member as less as possible, and a sprocket for a crawler belt used in the elastic crawler driving apparatus.
It is an another object of the invention to provide a sprocket for a crawler belt capable of exerting uniform extension force to a wrapping portion of a tension member embedded in an elastic crawler.